Corrosion probe

ABSTRACT

The invention relates to a device and a method for determining the quality of the corrosion on the inside of a wall manufactured from non-corrosion-resistant material of a space in which corrosive conditions prevail, wherein at least one part of the wall is removable from the wall without destructive operations and is available after removal for examination outside the space. This measure has the advantage that an element to be removed without destructive operations can be removed easily and can be replaced. Although in the first instance a screw is envisaged, other embodiments are in no way precluded, such as a pin or a prop onto which another fixation device is arranged, for instance a bayonet fitting.

FIELD OF THE INVENTION

The present invention relates to a device and a method for determiningthe quality of the corrosion on the inside of a wall manufactured fromnon-corrosion-resistant material of a space in which corrosiveconditions prevail.

BACKGROUND OF THE INVENTION

Such a situation occurs for instance in steam boilers which are adaptedto feed for instance the steam turbines of an electric power station, aswell as in other types of device such as waste incinerators, boilersprovided with fire tubes and the like. In order to be able to estimatethe remaining life of the wall of such an installation it is of greatimportance to have information concerning the thickness and otherqualities of the usually inaccessible space in which such corrosiveconditions prevail. Particularly in the case of an electric powerstation this access is especially difficult since, in order to reach therelevant side of the wall, the unit in question of the electric powerstation has to be shut down. This causes great economic loss.

There also usually exists a need, for instance in the case ofirregularities in the process, for knowledge relating to the quality ofsuch an oxide layer.

According to the generally known prior art, a part of the wall of thespace is removed and replaced by a corresponding part, whereafter theremoved wall part can be examined. This has the drawback that on the onehand the unit has to be shut down and on the other removal andre-placing of a wall part entails high cost, caused on the one hand bythe length of time for which the installation must be shut down and onthe other by the necessary tests enabling the quality of the welds to bedetermined after placing of the replacement wall part.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide such a device andmethod, wherein the above stated drawbacks are avoided.

This objective is achieved in that at least one part of the wall isremovable from the wall without destructive operations and is availableafter removal for examination outside the space.

This measure has the advantage that an element to be removed withoutdestructive operations can be removed easily and can be replaced.

Although in the first instance a screw is envisaged, other embodimentsare in no way precluded, such as a pin or a plug onto which anotherfixation device is arranged, for instance a bayonet fitting.

However, in the case of a water tube boiler where the walls are formedat least partially by water tubes, it is important that the heattransfer process taking place in the tubes, and thus the flow of liquidor gas through the tubes, may not be interrupted. It is thereforeprudent to make such an element as small as possible. The removable wallpart is then preferably formed by a bolt screwed into an openingarranged in the wall and provided with screw thread.

It is then also important that the opening is arranged in the stripbetween two water tubes.

In order to achieve that the corrosion occurring on the bolt has thesame quality as the corrosion occurring on the other wall parts, it isimportant that the bolt be manufactured from the same material as thewall. This reproducibility is improved when the bolt is screwed into theopening up to a position in which the end of the screw thread of thebolt lies flush with the inner side of the wall.

In order to obtain a good resemblance between the oxide development onthe actual wall and the bolt, it is important that the temperature ofthe bolt is substantially equal to that of the wall. The strips betweenthe water tubes of the water tube boiler will have a slightly highertemperature than the tube walls because the tube walls are anyway cooledby the water flowing through the tubes, so that there is no case inwhich less oxidation occurs on the bolt surface.

To be able to make a comparison between a non-affected part of theexposed surface and an indeed affected part thereof, a part of thesurface exposed to the core of the space concerned is covered by a layerof a precious metal, like gold or platina.

So as to prevent wear of the screw thread in the case of repeatedscrewing in and out of the bolts, the opening is preferably providedwith a helicoil.

It is further noted that due to the simplicity of the present inventionit becomes possible to repeatedly carry out an examination into thesituation of the oxide layer, since the difficulty involved and theaccompanying interruption of the operating process is extremely small.During the examination the removed part is preferably sawn through inthe direction transversely of the plane of the wall, whereafter it canbe inspected visually or microscopically. It will be apparent that thisinspection becomes clearer when the sawn surface is polished. Thepolished surface is photographed in order to record the results of theexamination and to enable comparison with corrosion in other situations,for instance at other locations in the same boiler, with other boilersin similar conditions, with other fuels, with the corrosion situation atan earlier or later stage. It is then possible for the photographicimage of the polished surface to be converted to digital form andquantified. This provides the option of electronic processing of theresults and of determining, for instance by planimetry, a rough estimateof the thickness and quality, such as porosity and sulphide content, ofthe oxide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be elucidated hereinbelow with reference tothe annexed figures, in which:

FIG. 1 shows a partly broken away perspective view of a tube wall of awater tube boiler in which probes according to the present invention areapplied;

FIG. 2 shows a sectional view of a part of a tube wall in which isarranged a probe according to the present invention; and

FIG. 3 shows an enlarged photo of a probe according to the invention inwhich the oxide layer is clearly visible.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 1 is a tube wall 1 which forms part of a water tube boilerof for instance an electric power plant. Tube wall 1 is formed by tubes2 in which flows water or steam which is heated by the combustionprocess in the water tube boiler. FIG. 1 shows the inner side of thewall in question where the oxidation process occurs. Tubes 2 aremutually connected by strips 3 which have been created by weldingtogether tubes 2.

As can be seen, a hole 4 is drilled in a number of the strips 3, intowhich hole is placed a bolt 5. Bolt 5 is preferably manufactured fromthe same material in which the tube wall is manufactured. Bolt 5 isscrewed into hole 4 to a depth such that the end of the shank 6 of thebolt lies flush with the level of the inner surface of tube wall 1.

When an inner side of such a tube wall must be examined for oxidation,for instance as a consequence of periodic inspection or as a result ofirregularities occurring inside the boiler, bolt 5 is loosened, replacedby a similar bolt, whereafter the end surface 6 of the bolt can beexamined. A normal visual inspection is of course possible here first ofall, while it is advantageous to saw through such a bolt in the lengthso that a cross-section of the oxide layer is obtained.

The presence of the protecting layer in the form of a layer of aprecious metal allows a comparison between an affected surface and anon-affected surface.

This can in turn be examined, possibly after polishing thereof,whereafter visual inspection or microscopic examination can once againtake place. Such cross-sections are herein photographed. FIG. 3 shows anexample thereof.

Finally, it is possible to scan such a photo and put it in digital form,whereafter the thus obtained image can be subjected to electronicprocessing methods, for instance quantifying methods.

The simplicity of this inspection method enables such an inspection tobe repeated periodically with relatively great frequency, so thatchanging conditions can be taken into account, for instance a change infuel, different setting of burners and so on. It is moreover possible,as shown in FIG. 1, to arrange such probes at different locations lyingclose to one another; reproducibility of the process is herebyincreased, while it is also possible to arrange temperature sensors inthe vicinity of the probes to make it possible to determine a relationbetween corrosive behaviour and temperature. The temperature sensors arepreferably connected to recording equipment.

It is of course also possible to arrange such probes at diverselocations in the boiler lying further apart. More information is herebyalso obtained concerning corrosivity of the flue gases at diverselocations and heights in the boiler.

What is claimed is:
 1. Method for inspecting the quality of thecorrosion on the inside of a wall of a water tube boiler manufacturedfrom non-corrosion-resistant material of a space in which corrosiveconditions prevail, comprising removing at least one part of the wall ofthe water tube boiler by means of non-destructive operations andsubsequently subjecting the removed wall part to examination outside thespace, wherein the part of the wall comprises a bolt having a shankhaving an end flush with the inside of the wall and wherein the end isexposed to the space.
 2. Method as claimed in claim 1, furthercomprising replacing the part of the wall with a correspondingreplacement part by non-machining operations.
 3. Method as claimed inclaim 1, further comprising examining the end exposed to the space. 4.Method as claimed in claim 3, further comprising comparing the part ofthe bolt exposed to the space with another part thereof.
 5. Method asclaimed in claim 1, further comprising sawing the removed part in thedirection transversely of the plane of the wall and then inspecting theresulting sawn surface.
 6. Method as claimed in claim 5, furthercomprising polishing the sawn surface prior to inspecting.
 7. Method asclaimed in claim 6, further comprising photographing the polishedsurface to form a photographic image.
 8. Method as claimed in claim 7,further comprising converting the photographic image to digital form andquantifying the digital form.
 9. A wall of a water tube boilermanufactured from non-corrosion resistant materials comprising aremovable wall part attached to the wall for determining the quality ofcorrosion on the inside of the wall, wherein the wall encloses a spacein which corrosive conditions prevail, wherein the wall is formed atleast partially by water tubes, wherein the removable wall part isremovable from the wall without destructive operations to allow the wallto be inspected outside the space, wherein the removable wall part isformed by a bolt screwed into an opening in the wall, wherein theopening is between two water tubes and the bolt is screwed into theopening up to a position in which the end of the bolt exposed to thespace lies flush with the inner side of the wall, wherein the boltcomprises the same material as the wall and is coated with a layer of aprecious metal at least at the end of the bolt exposed to the space. 10.The wall as claimed in claim 9, wherein the precious metal is gold orplatinum.
 11. The wall as claimed in claim 9, wherein the opening isprovided with a helicoil.